The present invention relates to a magnetic disc and a data writing/reading-out method, and more specifically, to a magnetic disc for conducting data writing/reading-out by a contact start and stop (CSS) system, as well as a data writing/reading-out method.
Usually, writing and/or reading-out information to/from a magnetic disc is conducted by a magnetic head. In a hard disk drive, the magnetic disc is rotated at a high speed to fly the magnetic head. In the magnetic disc, mechanical polishing is applied substantially concentrically with a circumferential direction of a magnetic disc to form a fabrication trace (texture pattern) on the surface thereof (hereinafter referred to as "mechanical texture") for improving a magnetic characteristic. Usually, the mechanical texture is applied on the surface of a non-magnetic substrate or on an underlayer composed of Ni--P or Cr disposed on the substrate.
Along with the increasing of the amount of information, and the demand for miniaturizing and light-weightening the storage device, the linear recording density and the track density are increased, so that scratches caused by the existent mechanical texture result in an error at a high probability. Therefore, it has been proposed a method of applying the mechanical texture only in a zone where a contact start and stop operation is conducted (CSS zone) at the inner circumference of the magnetic disc while leaving a data recording zone (data zone or data writing zone) as it is. However, the surface of the data zone is made higher than that of the CSS zone, ad since it is difficult to moderate the difference between the data zone and CSS zone into a smooth inclination, there arises a problem that the magnetic head crushes upon seeking.
Further, a method of preparing a texture pattern by laser beam (laser texture) has also been proposed instead of the mechanical texture. For instance, U.S. Pat. Nos. 5,062,021 and 5,081,781 propose an attempt of locally melting a Ni--P layer by a Q switch laser beam of Nd--YAG having a very narrow pulse width and an very high energy density and forming a crater-like projection, thereby improving the CSS characteristic with respect to the magnetic head by the circular rim thereof.
According to the laser texture described above, the texturing can be applied only to the CSS zone of the magnetic recording medium. However, at least a certain height is required for the projections in the CSS zone in order not to cause sticking between the magnetic head and the disc, so that the glide height of the head is determined by the height of the projection. Accordingly, since the glide height of the recording medium is defined by the glide height in the CSS zone, the flying height of the head is excessive in the data zone to bring about a problem that the recording density can not be improved satisfactorily.
It is, accordingly, important in the data writing/reading-out method of a magnetic disc of the how the stable flying height of the magnetic head is lowered in the data zone or how sticking is suppressed at a stop position of the magnetic zone.
As a result of the present inventors' studies, it has been found that by using a disc drive having a magnetic head for writing/reading-out data from/to a magnetic disc, while flying the magnetic head at a predetermined flying height, which the magnetic disc comprising a contact start and stop (CSS) zone comprising a taking-off/landing region and a stopping region, for a contact start and stop operation of the magnetic head and a data zone for writing/reading-out data, wherein a plurality of projections are present in the CSS zone, the height of the projections in the taking-off/landing region decreases from inner to outer in a radial direction of the disc, an average gradient for the height of the projections in the taking-off/landing region is 1.times.10.sup.-6 to 5.times.10.sup.-5, the maximum height of the projections in the CSS zone is higher than a flying height of a magnetic head in the data zone, and the minimum height of the projections in the CSS zone is lower than the flying height of the magnetic head in the data zone, the magnetic head can conduct a stable CSS operation while seeking. The present invention has been attained on the basis of the finding.